cpupower: Add cpuid cap flag for MSR_AMD_HWCR support

Remove the family check for accessing the MSR_AMD_HWCR MSR and replace
it with a cpupower cap flag.

This update also allows for the removal of the local cpupower_cpu_info
variable in cpufreq_has_boost_support() since we no longer need it to
check the family.

Signed-off-by: Nathan Fontenot <nathan.fontenot@amd.com>
Reviewed-by: Robert Richter <rrichter@amd.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>